Light source with integrated monitor photodetector and diffuser

ABSTRACT

A light source includes a substrate with a first surface and an opposite second surface. An epitaxial layer is positioned on the first surface of the substrate. The light source also includes at least one light generator in the epitaxial layer positioned such that an optical signal transmitted thereby is directed toward the substrate. A diffuser is positioned on the second surface of the substrate, and at least one monitor photodetector is positioned in the epitaxial layer in an arrangement configured to receive a portion of the optical signal which is reflected by the diffuser. In one form, the light generator may include a vertical cavity surface emitting laser (VCSEL).

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/847,086 filed May 13, 2019, the contents of which areincorporated herein by reference in their entirety.

FIELD

The present disclosure generally relates to light sources which may, forexample, produce a laser. More particularly, but not exclusively, thepresent disclosure relates to a light source which may include avertical cavity surface emitting laser (VCSEL) and an integrated monitorphotodetector and diffuser.

BACKGROUND

Unless otherwise indicated herein, the materials described herein arenot prior art to the claims in the present application and are notadmitted to be prior art by inclusion in this section.

Light sources which produce lasers may be used in many differentapplications, ranging from communication components for datatransmission to 3D sensing technologies. One type of laser that is usedin optical data transmission and 3D sensing is a vertical cavity surfaceemitting laser (VCSEL). As its name implies, a VCSEL has a laser cavitythat is sandwiched between and defined by two mirror stacks. A VCSEL maybe constructed on a semiconductor wafer which may include a GalliumArsenide (GaAs) substrate. The VCSEL includes a bottom mirrorconstructed on the semiconductor wafer. Typically, the bottom mirrorincludes a number of refraction layers of alternating high and lowindices of refraction. As light passes from a layer of one index ofrefraction to another, a portion of the light is reflected. By using asufficient number of alternating layers, a high percentage of light canbe reflected by the mirror.

An active region that includes a number of quantum wells is formed onthe bottom mirror. The active region forms a PN junction sandwichedbetween the bottom mirror and a top mirror, which are of oppositeconductivity type (e.g., one p-type mirror and one n-type mirror).Notably, the notion of top and bottom mirrors can be somewhat arbitrary.In some configurations, light could be extracted through the substratefrom the wafer side of the VCSEL, with the “top” mirror being totallyreflective—and thus opaque, which are referred to as bottom emittingVCSELs. Other VCSELs can be top emitting or emitting opposite and awayfrom the substrate and wafer. As used herein, the “top” mirror refers tothe mirror that is opposite of the substrate and that reflects thelight, the middle is the active region, and the “bottom” refers to thesubstrate side of the active region that has the substrate from whichlight is to be extracted, regardless of how it is disposed in thephysical structure.

Some illumination functions benefit from a light source that issubstantially uniform in its profile. For example, a user may want toengineer the profile to be 30 degrees divergent in the horizontaldirection and 50 degrees in the vertical direction so a rectangular areais illuminated in the far field. Light sources implemented in suchillumination functions may include a diffuser or an engineered diffuser.The diffuser may control divergence of the profile of the light source.However, in these light sources the diffuser or the engineered diffuseris included in a package at some distance away from an optical source.Accordingly, including the diffusers in these light sources involvespackage-level integration and costs associated with the packageintegration.

The subject matter claimed herein is not limited to implementations thatsolve any disadvantages or that operate only in environments such asthose described above. Rather, this background is only provided toillustrate one example technology area where some implementationsdescribed herein may be practiced.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential characteristics of the claimed subject matter, nor is itintended to be used as an aid in determining the scope of the claimedsubject matter.

In one embodiment, a light source includes a substrate with a firstsurface and an opposite second surface. An epitaxial layer is positionedon the first surface of the substrate. The light source also includes atleast one light generator in the epitaxial layer positioned such that anoptical signal transmitted is directed toward the substrate. A diffuseris positioned on the second surface of the substrate, and at least onemonitor photodetector in the epitaxial layer is positioned to receive aportion of the optical signal which is reflected by the diffuser.

In another embodiment, a system includes a light source which includes asubstrate including a first surface and an opposite second surface; anepitaxial layer positioned on the first surface of the substrate; atleast one light generator in the epitaxial layer positioned such that anoptical signal transmitted thereby is directed toward the substrate; adiffuser positioned on the second surface of the substrate; and at leastone monitor photodetector in the epitaxial layer positioned to receive areflected optical signal which is reflected by the diffuser. The systemalso includes a controller operably coupled with the at least one lightgenerator and the at least one monitor photodetector. The controller isstructured to control operation of the at least one light generatorbased on the reflected optical signal received by the at least onemonitor photodetector.

In yet another embodiment, a method of preparing a light source includesproviding a substrate having a first surface and a second surfacepositioned opposite of the first surface; forming an epitaxial layer onthe first surface of the substrate; forming at least one light generatorin the epitaxial layer; forming at least one monitor photodetector inthe epitaxial layer; and forming a diffuser on the second surface of thesubstrate.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by the practice of the invention. Thefeatures and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the present inventionwill become more fully apparent from the following description andappended claims, or may be learned by the practice of the invention asset forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent invention, a more particular description of the invention willbe rendered by reference to specific embodiments thereof which areillustrated in the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope. The invention willbe described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIG. 1 is a schematic illustration of a vertical cavity surface emittinglaser (VCSEL);

FIG. 2 is a schematic, partial section view of one embodiment of a lightsource including a VCSEL;

FIG. 3 is a schematic, partial section view of an alternative embodimentof a light source including a VCSEL;

FIG. 4A is a schematic, plan view of another alternative embodiment of alight source including an array of VCSELs;

FIG. 4B is a schematic, plan view of another alternative embodiment of alight source including an array of VCSELs;

FIGS. 5 and 6 are section views illustrating different operating aspectsof a light source including an array of VCSELs; and

FIG. 7 is a schematic illustration of a system for operating a lightsource.

DETAILED DESCRIPTION

Reference will now be made to the drawings to describe various aspectsof example embodiments of the invention. It is to be understood that thedrawings are diagrammatic and schematic representations of such exampleembodiments, and are not limiting of the present invention, nor are theynecessarily drawn to scale.

The present disclosure generally relates to light sources which may, forexample, produce or provide a laser. More particularly, but notexclusively, the present disclosure relates to light sources which mayinclude a vertical cavity surface emitting laser (VCSEL) and anintegrated monitor photodetector and diffuser. Despite variousembodiments being described in the context presented herein, theembodiments disclosed herein may be employed in other fields oroperating environments where the functionality disclosed herein may beuseful. Accordingly, the scope of the invention should not be construedto be limited to the example implementations and operating environmentsdisclosed herein.

In one aspect, a light source includes a bottom emitting configurationthat includes a light generator region having a middle active regionbound by a top mirror and bottom mirror. The light generator region canhave a contact layer at the top end of the top mirror, where the contactlayer has a reflecting region that reflects the light toward the bottomemitter end. The bottom emitting configuration may include a VCSEL asthe light generator and may be considered to be a substrate emitter dueto the light being emitted through the substrate that is typicallyconsidered the bottom of the VCSEL. The light source may include adiffuser integrated with the substrate. For example, the diffuser may beintegrated with the bottom side of the substrate opposite of the lightgenerator. The light source may also include a monitor photodetectorthat is integrated with the same substrate having the light generatorand diffuser integrated therewith so as to monitor light reflected fromthe diffuser. As such, the light source can be configured to include themonitor photodetector and light generator on the top surface of thesubstrate, and the diffuser is on the bottom surface of the substrate.

In one aspect, the light generator, diffuser, and monitor photodetectorcan be considered to be an integrated package. The light generator andmonitor photodetector can be prepared from layered semiconductormaterials, which may for example be in a semiconductor epitaxialstructure. The substrate may also be formed from a semiconductorepitaxial structure. The diffuser can be etched into the substrate, orit may be configured as an optically transmissive material, such as aglass or polymer material, that is integrated with the bottom surface ofthe substrate. The light generator and monitor photodetector can besubstantially similar in semiconductor epitaxial structure, but with themonitor photodetector having a reversed bias. In one form, the lightsource may include an array of two or more light generators (e.g.,individual VCSELs) with at least one, two, or more monitorphotodetectors on the top side of the substrate and at least onediffuser on the bottom side of the substrate.

The light sources described herein may include a number of differenttypes of semiconductor materials. Examples of suitable materials includeIII-V semiconductor materials (e.g., prepared from one or more Group IIImaterials (boron (B), aluminum (Al), gallium (Ga), indium (In), thallium(Tl), and ununtrium (Uut)) and one or more Group V materials (nitrogen(N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi) andununpentium (Uup)) and optionally some type IV materials.

The light sources may include the light generator and monitorphotodetector having an active region having one or more quantum wellsand optionally one or more quantum well barriers between adjacentquantum wells. The quantum wells and quantum well barriers can beseparated by one or more transitional layers therebetween. Thetransitional layers may also be referred to as interfacial layers asthey are located at the interface between the quantum wells and quantumwell barriers. However, other variations are possible.

Electrical confining layers may optionally sandwich the active regionand provide optical gain efficiency by confining carriers to the activeregion. The confining layers can have a region of high energy band gapwhich in the case of many III-V compounds translates to high aluminumcontent (e.g., 70%-100% Al for the type III material). The aluminumcontent can be selected to give the material a relatively wide band gap,as compared to the band gap in the quantum well barriers of the activeregion. The wide band gap material can give the confining layer goodcarrier confinement and increases the efficiency in the active region.In an exemplary embodiment, the high aluminum region may also include anincrease in doping. The confining layer can be doped with a p-type orn-type dopant depending on whether the confinement barrier is on then-side or p-side of the active region.

Referring now to FIG. 1 , one non-limiting configuration of a bottomemitting VCSEL 100 includes periodic layer pairs for a top mirror stack124 and a bottom mirror stack 116. The VCSEL 100 includes an isolationregion 128 adjacent to the top mirror stack 124. Forms in which anisolation region is additionally or alternatively present adjacent tothe bottom mirror stack 116 are possible, as well as forms where noisolation regions are present adjacent to the top mirror stack 124 andthe bottom mirror stack 116.

The VCSEL 100 includes a substrate 114 which may be doped with animpurity such as a p-type dopant or an n-type dopant. A diffuser 112 isintegrated with a bottom surface of the substrate 114 and the bottommirror stack 116 is formed on an opposite side of the substrate 114. TheVCSEL 100 includes a bottom confining layer 118 formed on the bottommirror stack 116, although forms where the bottom confining layer 118 isnot present are possible. An active region 122 is formed over the bottomconfining layer 118, although the active region 122 may be formed overthe bottom mirror stack 116 when the bottom confining layer 118 is notpresent. A top confining layer 120 is formed over the active region 122,although forms where the top confining layer 120 is not present arepossible. In the illustrated form, the active region 122 may beconsidered to be sandwiched between the bottom confining layer 118 andthe top confining layer 120.

The isolation region 128 is formed over the top confining layer 120, butmay be formed over the active region 122 in forms where the topconfining layer 120 is not present. In addition, an isolation region maybe positioned under the active region 122 when the bottom confininglayer 118 is not present, or under the bottom confining layer 118 whenit is present. The isolation region 128 includes a lateral blockingregion 127 and a central conductive channel region 129. The bottomconfining layer 118, the top confining layer 120, or both the bottomconfining layer 118 and the top confining layer 120 may be a spacerregion between the active region 122 and the isolation region 128.Alternatively, the bottom confining layer 118, the top confining layer120, or both the bottom confining layer 118 and the top confining layer120 may be a conductive region. Thus, any spacer region bounding theactive region 122 may be a confining region, conductive region, orsemiconductor spacer that is not confining or conducting. The top mirrorstack 124 is formed over the isolation region 128. A metal contact layer126 forms a contact on a portion of the top mirror stack 124.

The bottom mirror stack 116 and the top mirror stack 124 may bedistributed Bragg reflector (DBR) stacks, and include periodic layerssuch as layers 132 and 134. The periodic layers 132 and 134 may beAlGaAs and AlAs, respectively, but may also be made from other III-Vsemiconductor materials. The top mirror stack 124 and the bottom mirrorstack 116 can be doped or undoped and the doping can be n-type or p-typedepending on the particular design of the VCSEL 100.

The metal contact layer 126 and any other metal contacts which may bepresent can be ohmic contacts that allow appropriate electrical biasingof the VCSEL 100. When the VCSEL 100 is forward biased with a voltage onmetal contact layer 126 different than the other contact (not shown),the active region 122 emits light, the light passes through the topmirror stack 124 and reflects off of the metal contact layer 126. In oneaspect, the light may reflect off of a metal body 150 of the metalcontact layer 126. Other configurations of contacts may be used togenerate a voltage across the active region 122 and generate a light oroptical signal 170 that is emitted from the bottom of the substrate 114,through the diffuser 112, or both.

In its bottom emitting arrangement, the top end of the VCSEL 100 mayinclude greater reflectivity relative to its bottom emitting end. Insome aspects, the bottom mirror stack 116 may have fewer mirror periodsthan the top mirror stack 124. The VCSEL 100 is further configured toemit light from the substrate 114 and through the diffuser 112. As such,the diffuser 112 may be at least partially translucent or transparent tothe light. In some aspects, the bottom surface of the substrate 114 mayinclude an anti-reflective coating.

Referring now to FIG. 2 , there is illustrated in section view anon-limiting configuration of a light source 200. The light source 200includes a VCSEL 100 and a pair of monitor photodetectors 250. Themonitor photodetectors 250 are positioned on a top or first surface 214of the substrate 114 opposite of the integrated diffuser 112 which ispositioned on an opposite, bottom or second surface 216 of the substrate114. Similarly, the VCSEL 100 is associated with the monitorphotodetectors 250 that are integrated with the substrate 114 whichincludes the VCSEL 100 and the integrated diffuser 112 in order tomonitor light reflected from the diffuser 112. The diffuser 112 may beintegrated at a chip-level with the substrate 114, other components ofthe VCSEL 100, and the monitor photodetectors 250. As illustrated, theVCSEL 100 may transmit an optical signal 170 which is directed towardand may propagate through the substrate 114; e.g., from the firstsurface 214 to the second surface 216.

The light source 200 includes an epitaxial layer 208 which may be formedon the first surface 214 of the substrate 114 and in which variouscomponents of the VCSEL 100 may be formed. Additionally, one or morecomponents of the VCSEL 100, such as the metal contact layer 126 may beformed on the epitaxial layer 208. The monitor photodetectors 250 mayalso be formed in the epitaxial layer 208.

In some embodiments, the light source 200 may include an array of VCSELs100. The array of VCSELs 100 may include multiple, individual VCSELs 100that are arranged to transmit the optical signal 170. The number ofVCSELs 100 may be based on a particular application for which use of thelight source 200 is intended. For instance, in some embodiments, thearray of VCSELs 100 may include many hundreds (e.g., one thousand ormore) of the individual VCSELs. The individual VCSELs 100 may beseparated by etched regions (not shown) to form mesas.

In these and other embodiments, the VCSELs 100 of the array of VCSELsmay be arranged in a pattern. The pattern of the VCSELs may berepetitive or may be arranged in a pattern that is symmetric about atleast one axis. For example, the VCSELs 100 in the array of VCSELs maybe arranged in a rectangular pattern that is symmetric about axes thatare substantially parallel to the X-axis or the Y-axis. Alternatively,in these and other embodiments, the VCSELs 100 of the array of VCSELsmay be arranged in a non-repeating or non-symmetric pattern. Forexample, the VCSELs 100 may be arranged in a random pattern or apseudo-random pattern.

As indicated above, the optical signal 170 is directed toward and maypropagate through the substrate 114, and as it does so the dimensions ofthe optical signal 170 may change. For instance, in the illustratedform, a diameter or a dimension in the Y direction of the optical signal170 may increase as the optical signal 170 propagates through thesubstrate 114.

The diffuser 112 may be positioned directly on the second surface 216 ofthe substrate 114. For example, a surface of the diffuser 112 and thesecond surface 216 may be in direct physical contact with one anothersuch that the optical signal 170 propagates directly from the substrate114 to the diffuser 112. Additionally or alternatively, the diffuser 112may be formed such that there is no distinction between the diffuser 112and the second surface 216 of the substrate 114. For example, in oneform, the diffuser 112 may be an etched grating formed in the secondsurface 216 of the substrate 114. Accordingly, the optical signal 170propagates through the diffuser 112 after the optical signal 170 exitsthe substrate 114 at the second surface 216.

The diffuser 112 is configured to control a particular cross-sectionalprofile of a beam 172 of the optical signal 170 which results after theoptical signal 170 propagates through the diffuser 112. Control of theparticular profile of the beam 172 may include diverging the opticalsignal 170 (as shown), converging the optical signal 170, collimatingthe optical signal 170, or some combinations thereof. Additionally,control of the particular profile of the beam 172 may include control intwo axes. For example, the particular profile of the beam 172 may becontrolled such that the particular profile includes a first dimensionin a first direction that is aligned with a first of the two axes (e.g.,the first direction may be parallel with the Y-axis) and a seconddimension in a second direction that is aligned with a second of the twoaxes (e.g., the second direction may be parallel to the Z-axis). Thecontrol may also result in any cross-sectional shape ranging fromcircular shapes to polygonal shapes, or random or abstract shapes asdesired, just to provide a few non-limiting examples.

The substrate 114 may be comprised of various materials or combinationof materials. The material(s) of the substrate 114 may dictate or may beselected to accommodate a wavelength of the optical signal 170. Forexample, in some embodiments, the substrate 114 may be comprised ofgallium arsenide (GaAs). A GaAs substrate may be suitable in embodimentsin which the optical signal 170 has a wavelength within the infrared(IR) spectrum such as a wavelength greater than about 900 nanometers(nm) (e.g., about 940 nm as an example). In other embodiments, thesubstrate 114 may be comprised of indium phosphide. In these and otherembodiments, the wavelength of the optical signal 170 may be longer thanthe wavelengths of embodiments using GaAs substrates. In yet otherembodiments, the substrate 114 may be comprised of gallium nitride,silicon carbide, or sapphire. In these and other embodiments, theoptical signal 170 may have a wavelength that may be in a blue spectrum.In yet other embodiments, the optical signal 170 may have a wavelengthof about 1300 nm. In one aspect, the beam 172 may have the samewavelength as the optical signal 170. The substrate 114 is configured tobe transparent to the wavelength range of the optical signal 170.

In the form shown in FIG. 2 , the diffuser 112 includes lenslets 111,only a few of which have been identified to preserve clarity. Thelenslets 111 as illustrated are spherical, but other shapes are alsocontemplated. The lenslets 111 are configured to provide the particularprofile of the beam 172 after the diffuser 112. For example, one or morecharacteristics of the lenslets 111 and the arrangement of the lenslets111 can be selected to provide a particular profile of the beam 172. Oneor more of the lenslets 111 may be refractive, and one or more of thelenslets 111 may be diffractive. In some embodiments, the lenslets 111may be positioned at random or pseudorandom locations on the secondsurface 216 of the substrate 114. Additionally or alternatively, thelenslets 111 may include two or more focal lengths which may be randomlyor pseudo-randomly determined. For example, the lenslets 111 may includefive individual lenslets or other integer of individual lenslets 111,each of which may have a different focal length.

Other forms for diffuser 112 are also possible as suggested above. Forexample, as shown in FIG. 3 , where like numerals refer to like featurespreviously described, a light source 200 a includes a diffuser 112 athat is formed by an etched grating integrated in the substrate 114. Assuch, the diffuser 112 a can be directly etched into the substrate 114or etched into a layer (e.g., an epitaxial layer) formed on thesubstrate 114. The diffuser 112 a can include etched gratings ofrandomly mixed grating pitch and orientation, ordered grating pitch andorientation, or other types of etched gratings. The features of thediffuser 112 a may be positioned on the second surface 216 of thesubstrate 114 randomly or pseudo-randomly.

The particular pattern of the features of the diffuser 112 or 112 a maybe repetitive or otherwise configured such that the VCSEL 100 need notbe precisely aligned with the diffuser 112 or 112 a. For example, insome VCSELs 100, a point of light emission 104 or region of lightemission may be precisely aligned with a diffuser so the diffuser maymodify or focus light passing therethrough. Misalignment between thepoint of light emission 104 and the diffuser may result in the lightbeing poorly focused. However, where the diffuser 112 or 112 a hasmultiple different characteristics, the point of light emission 104 maynot need to be precisely aligned therewith. For instance, in embodimentsin which the diffuser 112 or 112 a includes features which are randomlyor pseudo-randomly positioned and have random or pseudo-random focallengths may enable an imprecise alignment between the point of lightemission 104 and the diffuser 112.

While a majority of the optical signal 170 may emit through the diffuser112 or 112 a, some part of the optical signal 170 may be reflected backfrom the diffuser 112 or 112 a through the substrate 114 as reflectedlight 174 (e.g., as a reflected optical signal) toward the monitorphotodetectors 250. The reflected light 174 may be received by themonitor photodetectors 250 which in turn provide an electric signalindicative of the reflected light 174. Analysis of the electric signalprovided by the monitor photodetectors can determine if the diffuser 112or 112 a is operational (e.g., intact, positioned, and functioningproperly). The operational methods that analyze the electric signal ofthe reflected light 174 can provide an alert, such as an audio or visualalert, when it is determined that the diffuser 112 or 112 a has an issuelike being damaged or contaminated, or not functioning properly.

The monitor photodetectors 250 allow for real-time monitoring of thehigh diffraction order of the reflected light 174 from the backside ofthe diffuser 112 or 112 a. The monitor photodetectors 250 can beoperated by using reverse bias at the front side of the epitaxialmaterial, which will allow for automatic power control, and powershutdown of the VCSEL 100 for eye safety when there is failure of thediffuser 112 or 112 a.

The monitor photodetectors 250 may be any of a variety of differenttypes of photodetectors, such as photoemission, photoelectric, thermal,polarization, or photochemical types of photodetectors. The monitorphotodetectors 250 may sense light or other electromagnetic radiation,such as light having the wavelengths for the VCSELs 100 describedherein. In one form, the monitor photodetectors 250 may be configuredwith a p-n junction that converts light photons into electrical current.In some aspects, the absorbed photons of the reflected light 174 canmake electron-hole pairs in a depletion region for the electricalcurrent. In one aspect, the monitor photodetectors 250 are configuredwith a semiconductor epitaxial structure substantially similar or thesame as the VCSEL 100, but having a reverse bias applied thereto. Assuch, a monitor contact 252 may be associated with each of the monitorphotodetectors 250. The monitor photodetectors 250 may also have otherconfigurations that are known for monitor photodetectors such that theyare epitaxially different from the VCSEL 100. However, it should berecognized that having the monitor photodetectors 250 having the sameepitaxial structure as the VCSEL 100, and separated from the VCSEL 100(e.g., both as mesas with gaps therebetween), may simplify manufacturingprocesses. In one aspect, an etching protocol can be performed during amanufacturing process to form the VCSEL 100 and the monitorphotodetectors 250 as mesas.

While the light sources 200 and 200 a are illustrated with one VCSEL 100positioned between the monitor photodetectors 250, an array of VCSELs100, with any number of columns, rows, or distribution, may be locatedbetween the two monitor photodetectors 250. Additionally oralternatively, while the light sources 200 and 200 a each include a pairof monitor photodetectors 250, forms are possible in which a singlemonitor photodetector 250 is present or more than two monitorphotodetectors 250 are present. In one form, the VCSELs 100 and themonitor photodetectors 250 may be monolithically integrated with thesubstrate 114.

A device having the VCSEL 100 or operational circuitry, chips, or othercomponents of the device can be used to analyze the current generated bythe monitor photodetectors 250. The monitor photodetectors 250 generatea photo current of the reflected higher diffraction order beams from thediffuser 112 or 112 a.

In one aspect, the diffuser 112 or 112 a may generate multiple higherorder reflection beams (e.g., reflected light 174) back to the frontside of VCSEL wafers to the monitor photodetectors 250. The monitorphotodetectors 250 may be reversely biased for power monitoring of thereflected light 174. As the high diffraction order reflection may behighly sensitive to the structure of the diffuser 112 or 112 a,monitoring the average of multiple high diffraction order beams of thereflected light 174 with the monitor photodetectors 250 can provide theelectrical current having monitor data regarding power output level,power diffusion effectiveness, or other information for analysis. Theplacement of the monitor photodetectors 250 can be optimized based onthe design of the diffuser 112 of 112 a relative to the VCSEL 100.

The monitor photodetectors 250 may collect back reflected light from thediffuser interface on the other side of the substrate 114 in order tomonitor the light passing through the diffuser 112 or 112 a. The monitorphotodetectors 250 allow for constant real-time monitoring of thereflected light 174 so that a historical record of reflected light canbe recorded, which historical record of reflected light is indicative ofthe optical signal 170 emitted from the diffuser 112 or 112 a. If thereflected light 174 which is detected by the monitor photodetectors 250indicates a change in an optical characteristic or property, such as areduction of intensity, the electrical signals from the monitorphotodetectors 250 will change so that operation of the light source 200or 200 a may be modulated to accommodate the change. If for example thereflected light 174 falls below an operational threshold, the VCSEL 100may be turned off, or if an array of VCSELs are present, one or more ofthe VCSELs 100 responsible for the change in property may be turned off.In some instances, the diffuser 112 or 112 a may degrade or becomeunusable, which may result in turning off the VCSEL 100 or array ofVCSELs 100. In one form, the monitor photodetectors 250 may provide acontrol signal to a diver circuit that controls operations of the VCSEL100 or array of VCSELs 100 to alter operation of the VCSEL(s) 100dependent on the sensing conducted by the monitor photodetectors 250.

Amongst other things, the designs disclosed herein provide the abilityto monitor the functionality of the VCSEL(s) 100 as well as theintegrity of the diffuser 112 or 112 a. The designs disclosed herein mayalso provide higher reliability with respect to the integrated diffuser112 or 112 a compared to remotely placed (e.g., off chip) diffusers,along with the ability to monitor back reflection from the diffuser 112or 112 a in order to assess the functional integrity of the diffuser 112or 112 a, ranging from damage to the diffuser 112 or 112 a, decouplingor delamination of the diffuser 112 or 112 a from the substrate 114,contamination of the diffuser 112 or 112 a, or other issues. Themonitoring can be performed in real time so that any change to thefunctionality of the diffuser 112 or 112 a, identified by a change inback reflection sensed by the monitor photodetectors 250, may be readilyaddressed by changing one or more operational parameters.

While not previously mentioned, damaged or improperly functioningdiffusers can compromise eye safety. As such, the ability to monitor theintegrity of the diffuser 112 or 112 a allows use of the VCSEL 100 orVCSELs 100 to be discontinued to prevent optical leakage (e.g., errantlaser light) and potential eye damage.

Turning now to FIG. 4A, there is illustrated in top view a light source400 that includes a plurality of VCSELs 100 arranged in a VCSEL array402 of adjacent rows 406 (e.g., 12 rows of 11 VCSELs) between twomonitor photodetectors 250. The illustrated view shows the metal contactlayer 126 and the monitor contacts 252, with the epitaxial structurepositioned thereunder. The VCSELs 100 are arranged as mesas extendingfrom the first surface 214 of the substrate 114 with gaps therebetween.The metal contact layers 126 are electrically coupled to electricallines 404 that are arranged between adjacent VCSEL rows 406. The monitorcontacts 252 are also electrically coupled to electrical lines 408. Apower source and power conduction system (not shown) including theelectrical lines 404 and 408 can be included to power the VCSELs 100 andthe monitor photodetectors 250.

FIG. 4B illustrates a top view of a light source 450 having a VCSELarray 452 arranged between four monitor photodetectors 250. Theelectrical lines 404 are electrically coupled to electrical posts 410,and the electrical lines 408 are electrically coupled with electricalposts 412. A power conduction system 454 can include the electricallines 404 and electrical posts 410 separate from electrical lines 408and electrical posts 412. The power conduction system 454 can alsoinclude a corresponding set of electrical lines 414 and posts 416 thatare separate from both the electrical lines 404 and electrical posts 410and the electrical lines 408 and electrical posts 412. The powerconduction system 454 allows for individually operating the VCSELs 100and the monitor photodetectors 250. As can be seen, each pair ofadjacent VCSEL rows 406 may be operated independent of other pairs ofadjacent VCSEL rows 406. The monitor photodetectors 250 may also beoperated independently of each other.

The monitor photodetectors 250 can have a width (short side) and length(long side) that is suitable for the VCSEL array 452 for monitoring backreflected light. As shown, the width of the monitor photodetectors 250is about the same as the short dimension across two adjacent VCSEL rows406 with the electrical lines 404 therebetween. The length of themonitor photodetectors 250 is about the same as the long dimension forthe two adjacent VCSEL rows 406. However, other dimensions and shapes aswell as arrangements for the components may be used.

FIG. 5 illustrates a cross-sectional side view of a light source 500having a VCSEL array 502 between a pair of monitor photodetectors 250.Each VCSEL 100 is shown to have the metal contact layer 126 in a circuitwith a counter contact 504. Also, each monitor photodetector 250 isshown to have the monitor contact 252 in a circuit with a countercontact 506. Power can be applied appropriately for operation of theVCSELs 100 and monitor photodetectors 250.

The light emitted from the VCSELs 100 is shown by the dashed line arrows508 through the substrate 114 to the diffuser 112 a, and then beingemitted from the diffuser 112 a. The back reflected light is shown bythe solid arrows 510 from the diffuser 112 to the monitor photodetectors250. The monitor photodetectors 250 receive a reflected light signatureof the summation of the rays of reflected light, which provides a steadystate metric (e.g., value or range of suitable values) that can bemonitored. Any change in the steady state metric can provide anindication that there is a problem that needs to be solved, such asturning off all or part the VCSEL array 502.

During normal operation, the diffuser 112 a can widen the field of viewof the light emitted therefrom. At the same time, the higher orderreflection beams from the pattern of the diffuser 112 a reflect back tothe monitor photodetectors 250 for collection and measurement. Themonitor photodetectors 250 provide the feedback signal to an automaticpower control (APC) of the light source 500. The APC can be configuredso that the integrated monitor photodetectors 250 monitor for constantpower or operation of the light source 500 in a constant power mode.When there is a malfunction of diffuser 112 a or other malfunction(e.g., a VCSEL malfunction) as shown in FIG. 6 (where like numeralsrefer to like features previously described), there is a change in theback reflection to the monitor photodetectors 250 so that there is acorresponding change in the feedback signal provided to the APC. The APCcan then determine, such as with a microprocessor, the course of action.The course of action can range from turning off power to the entireVCSEL array 502, or selectively probing each VCSEL or VCSEL row todetermine the source of the problem, or whether the problem is at thediffuser level or the VCSEL level. In some aspects, the APC can shut offthe VCSEL array 502 for laser safety concerns.

While the forms of the light sources shown herein include the monitorphotodetectors positioned laterally outside of the VCSEL or VCSEL array,the monitor photodetectors can be in any lateral arrangement outside theVCSEL or VCSEL array, within the VCSEL array, or a combination thereof.

The VCSEL 100, array of VCSELs 100, and light sources 200, 200 a, 400,450 and 500 may be prepared by a manufacturing process that may includeforming the substrate and epitaxial layer, etching the epitaxial layerto form the VCSEL mesas and monitor photodetector mesas, forming theelectrical power conduction system, forming VCSEL circuits and monitorcircuits, and forming the diffuser on the substrate opposite of theVCSELs and monitor photodetectors.

The manufacturing process may also include forming a substrate; growinga first mirror region having a plurality of first mirror layers havingone or more indices of refraction and then (optionally) growing a firstspacer region over the first mirror region. An active region may then begrown over the first spacer region (or over the first mirror when afirst spacer region is not grown). An optional second spacer region ifpresent may be grown over the active region. An isolation region maythen be grown and formed over the second spacer region (or the activeregion when the second spacer region is not grown). The process may alsoinclude growing a second mirror region having a plurality of secondmirror layers having one or more indices of refraction. The epitaxialstructure is then etched to form the VCSELs in the array as mesas, andto form the monitor photodetectors as mesas. The metal layers for theVCSEL contacts and monitor contacts are formed on the VCSEL.

The active region or other portions of a VCSEL may be produced withmolecular beam epitaxy (MBE). Lower growth temperatures during the MBEcan be used to prepare the VCSEL semiconductor layers. The growth ofthese structures by MBE can be performed at <(less than) 500° C.Comparatively, the temperatures for metal organic chemical vapordeposition (MOCVD) can be >(greater than) 600° C. Additionally, theVCSELs can be prepared by methods that are similar to MBE, such as GSMBE(gas source MBE) and MOMBE (metalorganic MBE), just to provide a fewexamples.

In some embodiments, when the substrate 114 includes diffuser 112 a, itcan be etched at any time within the protocol to form the diffuser 112a. In forms where the substrate 114 includes the diffuser 112, thediffuser 112 may be mounted into a pre-formed recess in the substrate114, although other variations are possible.

A schematic illustration of a system 700 for operating a light source650 is illustrated in FIG. 7 , where like numerals refer to likefeatures previously described. While the following description isprovided in connection with the light source 650, it should beunderstood that it may also be applicable to the other light sources200, 200 a, 400, 450 and 500 disclosed herein. In the system 700, thelight source 650 includes an array of VCSELs 100, two monitorphotodetectors 250, and the diffuser 112 integrated with the substrate114 such as in one of the embodiments provided herein. During operationof the light source 650, the monitor photodetectors 250 may measurelight that is emitted from the VCSELs 100 through the substrate 114 andback reflected from the diffuser 112. If a change is detected in theback reflected light, then operation of the light source 650 may bealtered with a controller 702. For example, the controller 702 mayprovide an operation signal to the light source 650 and the monitorphotodetectors 250 may provide back reflection data to the controller702.

A processor 704 of the controller 702 may process the back reflectiondata (e.g., by executing a program stored in memory 706) and determinean operation level of the light source 650 based on the processed backreflection data. The operation level data may be saved as historicaloperation level data in a historical database 707 of the controller 702.The historical database 707 may be accessed to get historical operationlevel data that is compared with the back reflection data by theprocessor 704, such as in real time or in incremental time periods. Thehistorical operation level data can include a maximum operational levelthreshold and a minimum operational level threshold, either or both ofwhich can be defined or determined by continuously monitoring thehistorical operation level data and defining the thresholds based onsuitable operational data.

The real time operational data can be compared to the historical data,threshold data, or both, and the difference thereof can be determined.In instances where the difference is greater than a predefined value,the controller 702 may change operation of the light source 650, andwhen the difference is less than a predefined value, the controller maymaintain operation of the light source 650. The change in operation ofthe light source 650 can be implemented by changing power provided by apower system 710 to one or more of light source 650, the arrays ofVCSELs 100, individual VCSELs 100, and the monitor photodetectors 250,by a power controller 708 of the controller 702.

The change in operation of the light source 650 can include completelyshutting the light source 650 off, or systematically turning individualVCSELs 100 or groups of VCSELs 100 off and on to test whether any of theVCSELs 100 are functioning improperly. The light source 650 may beautomatically turned off to prevent light leakage and potential damageto the eye(s) of an operator. The operator may implement a test program,which may for example reside on the memory 706, that tests each of theVCSELs 100 and determines whether or not the respective VCSEL 100 isoperating within suitable levels. The operation of the light source 650can then either be terminated or adjusted to overcome faulty operation,including inoperability, of one or some of the individual VCSELs 100.The controller 702 may for example determine that the diffuser 112 hasbecome inoperable, contaminated, or otherwise compromised, and as aresult cease operation of the light source 650.

Unless specific arrangements described herein are mutually exclusivewith one another, the various implementations described herein can becombined to enhance system functionality or to produce complementaryfunctions. Likewise, aspects of the implementations may be implementedin standalone arrangements. Thus, the above description has been givenby way of example only and modification in detail may be made within thescope of the present invention.

With respect to the use of substantially any plural or singular termsherein, those having skill in the art can translate from the plural tothe singular or from the singular to the plural as is appropriate to thecontext or application. The various singular/plural permutations may beexpressly set forth herein for sake of clarity. A reference to anelement in the singular is not intended to mean “one and only one”unless specifically stated, but rather “one or more.” Moreover, nothingdisclosed herein is intended to be dedicated to the public regardless ofwhether such disclosure is explicitly recited in the above description.

In general, terms used herein, and especially in the appended claims(e.g., bodies of the appended claims) are generally intended as “open”terms (e.g., the term “including” should be interpreted as “includingbut not limited to,” the term “having” should be interpreted as “havingat least,” the term “includes” should be interpreted as “includes but isnot limited to,” etc.). Furthermore, in those instances where aconvention analogous to “at least one of A, B, and C, etc.” is used, ingeneral, such a construction is intended in the sense one having skillin the art would understand the convention (e.g., “a system having atleast one of A, B, and C” would include but not be limited to systemsthat include A alone, B alone, C alone, A and B together, A and Ctogether, B and C together, or A, B, and C together, etc.). Also, aphrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to include one ofthe terms, either of the terms, or both terms. For example, the phrase“A or B” will be understood to include the possibilities of “A” or “B”or “A and B.”

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. A light source, comprising: a substrate includinga first surface and an opposite second surface; an epitaxial layerpositioned on the first surface of the substrate; a plurality of lightgenerators arranged in a two-dimensional distribution in the epitaxiallayer, the light generators arranged in at least one column in a firstdimension and arranged in a plurality of rows in a second dimension,each of the light generators being positioned such that an opticalsignal transmitted is directed toward the substrate; a diffuserpositioned on the second surface of the substrate; and at least one pairof monitor photodetectors arranged in the epitaxial layer, the monitorphotodetectors in the at least one pair being arranged on both ends ofthe at least one column, a first of the monitor photodetectors in the atleast one pair being positioned to receive a first portion of theoptical signals transmitted from the light generators in the at leastone column and reflected by the diffuser, a second of the monitorphotodetectors in the at least one pair being positioned to receive asecond portion of the optical signals transmitted from the lightgenerators in the at least one column and reflected by the diffuser,wherein the light generators in each of the rows includes an array ofVCSELs, each of the arrays in the rows being arranged side-by-side inthe at least one column, each of the arrays being individuallycontrollable, wherein the two-dimensional distribution comprises aplurality of the at least one column of the light generators arranged inthe first dimension, each of the columns having the light generatorsarranged in the rows in the second dimension, and wherein the at leastone pair of the monitor photodetectors comprises a plurality of the pairof monitor photodetectors, each pair arranged on both ends of acorresponding one of the columns in the first dimension.
 2. The lightsource of claim 1, wherein the diffuser is etched directly into thesecond surface of the substrate.
 3. The light source of claim 1, whereinthe diffuser is directly coupled to the second surface of the substrate.4. The light source of claim 3, wherein the diffuser includes one ormore lenslets positioned on the second surface of the substrate.
 5. Thelight source of claim 1, wherein the monitor photodetectors in the atleast one pair are positioned at both ends of the at least one columnlaterally of the VCSELs in the rows.
 6. The light source of claim 1,wherein operation of each of the VCSELs in the array is individuallycontrollable.
 7. The light source of claim 1, wherein each of themonitor photodetectors is configured to provide an electrical signalindicative of the reflected optical signals.
 8. The light source ofclaim 1, further comprising a controller operably coupled with the lightgenerators and the at least one pair of the monitor photodetectors,wherein the controller is structured to control operation of the lightgenerators based on the reflected optical signals received by themonitor photodetectors.
 9. The light source of claim 8, wherein thecontroller is structured to terminate operation of one or more of thelight generators if a characteristic of the reflected optical signalsreceived by at least one of the monitor photodetectors of the at leastone pair deviates from a predetermined value for the characteristic. 10.The light source of claim 8, wherein a power system is operably andindividually coupled with each of the light generators; and wherein thecontroller is structured to individually control operation of each ofthe light generators with the power system.
 11. The light source ofclaim 8, wherein a power system is operably and individually coupledwith each of the monitor photodetectors, and wherein the controller isstructured to individually control operation of each of the monitorphotodetectors with the power system.
 12. The light source of claim 8,wherein in response to determining one or more of the light generatorsis functioning improperly based on the reflected optical signalsreceived by at least one of the monitor photodetectors, the controlleris structured to automatically terminate operation of the one or morelight generators.
 13. The light source of claim 1, further comprising acontroller operably coupled with the light generators and the at leastone pair of the monitor photodetectors, wherein the controller isstructured to control operation of the light generators at least in eachof the at least one column based on the reflected optical signalsreceived by the monitor photodetectors in the pair associated with theeach of the at least one column.
 14. The light source of claim 13,wherein the controller monitors a steady-state metric of at least eachof the columns of the light generators based on a summation of thereflected optical signals received at the monitor photodetectors in thepair associated with the each of the least one column.
 15. A method ofpreparing a light source, comprising: providing a substrate having afirst surface and a second surface positioned opposite of the firstsurface; forming an epitaxial layer on the first surface of thesubstrate; forming a plurality of light generators in a two-dimensionaldistribution in the epitaxial layer by arranging the light generators inat least one column in a first dimension and in a plurality of rows in asecond dimension and positioning each of the light generators such thatan optical signal transmitted therefrom is directed toward thesubstrate; forming at least one pair of monitor photodetectors in theepitaxial layer by arranging the monitor photodetectors of the pair atboth ends of the at least one column; and forming a diffuser on thesecond surface of the substrate such that a first of the monitorphotodetectors in the at least one pair is positioned to receive a firstportion of the optical signals transmitted from the light generators inthe at least one column and reflected by the diffuser, and such that asecond of the monitor photodetectors in the at least one pair ispositioned to receive a second portion of the optical signalstransmitted from the light generators in the at least one column andreflected by the diffuser, wherein the light generators in each of therows includes an array of VCSELs, each of the arrays in the rows beingarranged side-by-side in the at least one column, each of the arraysbeing individually controllable, wherein the two-dimensionaldistribution comprises a plurality of the at least one column of thelight generators arranged in the first dimension, each of the columnshaving the light generators arranged in the rows in the seconddimension, and wherein the at least one pair of the monitorphotodetectors comprises a plurality of the pair of monitorphotodetectors, each pair arranged on both ends of a corresponding oneof the columns in the first dimension.
 16. The method of claim 15,wherein forming the diffuser includes directly etching the diffuser intothe second surface of the substrate.
 17. The method of claim 15, whereinforming the diffuser includes directly positioning the diffuser on thesecond surface of the substrate.
 18. The method of claim 15, furthercomprising forming a first metal contact layer on the epitaxial layerand a second metal contact layer on the epitaxial layer.